There are many uses for vessels which may be required to withstand high internal pressures, say up to 5000 p.s.i., whether in the laboratory or in industry. One example is a decompression chamber for deep-sea divers, which chamber requires a power source to operate equipment therein, such as rotary gas pumps for circulating the breathing gas mixture through chemical carbon dioxide scrubbers to remove the carbon dioxide. For safety reasons it is not practical to use electric motors within the chamber and hence an external drive for motors within the chamber is required. Hermetically sealed drives using electric motors wherein the driven shaft projects through an opening in the chamber wall and is held in a pressurized zone have been utilized (see our Canadian patent application Ser. No. 226,097 filed May 2, 1975). Other types of external drives have been utilized, for example drives where the input shaft (external) is magnetically coupled to the output shaft (internal). Such drives have not been completely satisfactory since it is necessary to use a high pressure gas barrier between the input and output magnets and, when a metallic barrier to withstand the high pressures is used, eddy currents are set up which can cause substantial heating of the barrier and attendant losses in efficiency of the magnetic coupling. Additional cooling is therefore required for the gas barrier and in the past it has been necessary to provide add-on blowers or fans for the magnetic interface.